Heinz Peter Bredow said, "Regarding the so
called "three-meter gap" [beneath the K/T iridium layer]. This gap shrinks if
additional footprint data of dinosaurs is available. Footprints seems to be more
acid resistant than fossil bones....Martin Lockley described such a case for a
site in southeastern Colorado in "Tracking [Dinosaurs, 1991, page 202]".

That brings to mind an interesting
consideration: In the instance Lockley describes, the ornithopod
footprints were only 37 cm below the iridium layer, and, as we know, to date, no
dinosaur bones have been found equally near the K/T (iridium) layer. It is
HPB's statement that, "Footprints seems to be more acid resistant than fossil
bones", that really 'hits home' with me.

Why? Other than Early Cretaceous
natural casts of bones that have disintegrated, most all of the bones and teeth
found in this area of Maryland are those preserved in the very protective (from
acid ground waters in this quite swampy area) Arundel
clay.

That makes me wonder if the paucity of
dinosaurian (and other) bones immediately beneath the K/T iridium layer might
be, in large part, due to the intensely acid rain that would undoubtedly have
resulted from the impact event, soaking down into bone-bearing layers and
dissolving such materials.

Point of this story? Aside from watching for footprints, I suggest paleontologists keep
a more careful outlook for natural casts of dinosaur
(and other) bones (and teeth) within reasonable distances below the iridium
layer. Natural casts of bones and teeth are
much more difficult to notice and identify than are silicified natural bones and
teeth, and they may be the only evidence that is left of these items in many
immediately sub-K/T areas. If such casts are there, finding
them could shed considerable light on immediately pre-impact vertebrate
diversity, etc.

Ray Stanford

"You know my method. It is founded upon the observance
of trifles." -- Sherlock Holmes in The Boscombe Valley Mystery

> In talking with Dean Pearson at the PTRM, the
three-meter gap is shrinking > bit by bit, and it may just be a
statistical effect. I'm not sure how valid > this is or not, as I
usually avoid the whole K/T problem.

Regarding the so called
"three-meter gap". This gap shrinks if additional footprint data of dinosaurs
is available. Footprints seems to be more acid resistent than fossil bones.

Martin Lockley described such a case for a site in southeastern
Colorado in "Tracking Dinosaurs" (1991 page 202):

>> ... the
recent discovery of tracks right at the Cretaceous-Tertiary boundary, only
37 centimeters, about one foot, below the famous iridium layer (Fig. 15.1).
This layer, caused by fallout from a major catastrophic event, perhaps
impact with a meteorite or a volcanic eruption, marks the end of the
Mesozoic Era, the end of the Age of Dinosaurs (1). For over a decade earth
scientists have argued about whether the dinosaurs died out gradually
before the end of the era or suddenly at the time of the purported
catastrophe. Since there are no com- plete or partial skeletons of
dinosaurs in strata for at least three meters below the iridium layer,
paleontologists speak of a three-meter gap (2).

However, the discovery
of tracks 37 centimeters below the iridium has narrowed the gap to only
one tenth of its previous magnitude. The tracks are indisputable proof of
live dinosaurs, in this case duckbills, living later in the Cretaceous than
was previously proven. A simple discovery of a few tracks (Fig. 15.2)
improves our resolution of dinosaur data at the Cretaceous-Tertiary
boundary by an order of magnitude (3).

Footnotes:

1.
Iridium, a rare platinum-group metal that occurs in extraordinary
abundance at the Cretaceous-Tertiary boundary, it is thought to be
related to an event that caused widespread extinction at this time.
Since tracks are evidence of live dinosaurs, documentation of tracks
either above or below the Cretaceous-Tertiary boundary provides firm
evidence of the activity of living animals.

2. There are many
references to the "three-meter gap." David Raup devotes a whole chapter to
it in his book on the extinction debate. Raup, D. M. 1986. The Nemesis
Affair. New York: w. W. Norton, 220 pp.

3. The author discovered these
tracks in 1989. A detailed report is currently in preparation.
<<